An advanced Russian government cyber-espionage unit has been exploiting a known Exim email server vulnerability since August 2019, according to an NSA security alert.
The NSA said the Russian hackers are part of the GRU Main Center for Special Technologies (GTsST), field post number 74455, and it believes the group has been leveraging the unpatched critical vulnerability (CVE-2019-10149) in Exim servers to gain remote control over affected machines and potentially conduct espionage operations.
While the patch for addressing the vulnerability introduced in Exim version 4.87 has been available since June 5, 2019, many systems likely remain unpatched. By exploiting it, attackers gain the ability to add privileged users, alter network security settings, modify SSH configuration for remote access, and even deploy additional exploitation tools.
“When CVE-2019-10149 is successfully exploited, an actor is able to execute code of their choosing,” reads the NSA security alert. “When Sandworm exploited CVE-2019-10149, the victim machine would subsequently download and execute a shell script from a Sandworm-controlled domain.”
The group, known as “Sandworm,” is believed to have also developed the BlackEnergy malware responsible for Ukraine’s power outage in 2015 and 2016, and the NotPetya ransomware that targeted Ukraine in June 2017.
While it is unclear what damages the attacks could have inflicted or what public or private organizations might have been targeted, it is not the first time the NSA hasn’t shied away from pointing the finger at Russian, Chinese, Iranian, and North Korean operations.
The advisory also urges IT security and administrators to patch their systems, deploy defense-in-depth strategies and use network-based security appliances capable of detecting and blocking exploits.
“Update Exim immediately by installing version 4.93 or newer to mitigate this and other vulnerabilities. Other vulnerabilities exist and are likely to be exploited, so the latest fully patched version should be used,” warns the NSA security alert.